Method of assembling an electrical heating unit of the liquid immersion type



March 12, 1957 N J BURGER 2,785,270

METHOD OF ASSEMLI'NG AN ELECTRICAL HEATING UNIT OF THE LIQUID IMMERSION TYPE Filed July 9, 1954 n l IZ fwmfgk15. v i telt: 1 1 I E i E INVENTOR. N/cHoLns u? Hakes/a BY/,AMM mi Arron/KEY United States Patenti@ Frice METHOD F ASSEMBLING AN ELECTRICAL HEATING UNIT 0F THE LIQUID IMMER- SION TYPE Nicholas J. Burger, Montgomery County, Md., assigner to Electro-Therm, Incorporated, Silver Spring, Md.

Application July 9, 1954, Serial No. 442,245

12 Claims. (Cl. 21g-38) This invention relates to electrical heating units, and more particularly to a method of assembling an electrical heating unit of the liquid immersion type.

A main object of the invention is to provide a novel and improved method of pressure-sealing an electrical heating unit to a cover plate, said method providing an electrically insulated, completely liquid-tight seal between the cover plate and the heating unit, as well as providing a secure mechanical connection therebetween.

A further object of the invention is to provide an improved method of assembling an insulated electrical heating unit of the liquid immersion type, the method being capable of performance by the use of very simple apparatus and providing a substantial saving in time and costs, as over previous methods of assembling such heating units.

A still further object of the invention is to provide an improved method of pressure-sealing an electrical heating unit to a cover plate and at the same time electrically insulating the unit with respect to the plate, the method utilizing the compression-resisting characteristics of the densiiied granular insulating material employed internally in the heating unit as well as the physical characteristics of the external insulating material, whereby the outer Wall portion of the heating unit may be deformed by pressure transmitted thereto by a body of such external insulating material without causing the inner wall portion of the heating unit to be deformed inwardly.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

Figure l is a side elevational view, partly in longitudinal cross-section, of an electrical heating unit constructed in accordance with the improved method of the present invention.

Figure 2 is a cross-sectional detail View taken on line 2-2 of Figure l.

Figure 3 is an enlarged longitudinal cross-sectional view taken through the end portion of one of the arms of the heating unit during the assembly of the unit, and showing the pressure-sealing dies in position for pressuresealing the cover plate of the unit to said one of the arms.

Figure 4 is a cross-sectional view similar to Figure 3, but showing the relationship of the elements or Figure 3 at the end of the pressure-sealing step.

Figure 5 is a fragmentary side elevational view, partly in cross-section, showing the terminal end portion of an electrical heating unit constructed in accordance with a modification of the improved method of this invention.

Referring to the drawings, and more particularly to Figures 1 and 2, the electrical heating unit is designatedV generally at 11 and comprises a U-shaped tube 12 of suitable malleable metal, such as copper, brass, or the like, in which is positioned a helically wound heater wire 13 having rod-like end terminals 14. The heater wire 13 and its terminals are embedded in a densely compacted mass of powdered heat-refractory insulating m'a` terial 15, such as powdered magnesium oxide, or the like.

Secured to the ends of the rod-like members 14 are theA terminals 35, said terminals being of suitable malleable metal, such as copper, brass, or the like and being formed with axial bores receiving the rod-like members 14. The terminals are rigidly clamped to the rod-like members 14 by being compressed inwardly to define the dat surfaces 16, said flat surfaces defining a substantially square cross-sectional shape for the terminals thereat. resisting ceramic spacers 17 of porcelain or the like are interposed between the terminals 35 and the ends of the tubular member 12.

Designated at 18 is a relatively thick cover plate of malleable metal, such as copper, brass, or the like, secured to the end portions of the arms of the tubular member 12, as shown. The cover plate 18 may be of any suitable shape, and is adapted to overlap the margins of an opening in the boiler or other liquid tank to be heated, and may be provided with apertures 19 for bolting same to the tank. As shown at 20, the cover plate may be formed with a circular thickened central portion adapted to tit into a circular opening in the tank. The end portions of the tubular member are secured to the cover plate Within said circular thickened portion.

The cover plate 1S is pressure-sealed to the end portions of the tubular member 12 to provide electrically insulated, liquid-tight, mechanically rigid joints, without requiring any heat-employing processes. As shown in Figure l, the end portions of the tubular member enten-d through insulating sleeves 36, 36 secured in respective openings in the cover plate, and the metal of the cover plate and the material of the insulating sleeves 36 are deformed inwardly, causing the wall thickness of the; tubular member to be locally reduced at 21 over a substantial length along the tubular member. Due to the rock-like density of the internal insulating material 15, no inward deformation of the wall of the tubular member occurs. I

The insulating sleeves 36 are of relatively deformable material such as plastic, fiber, or the like, and are preferably suitably confined during the pressure-sealing process, as will be presently described, so that pressure is transmitted therethrough from the metal of the cover plate to the wall of the tubular member to cause the wall thickness of the tubular member to be reduced.

Referring now to Figures 3 and 4, the means for pressure-sealing the cover plate 1S to an end portion of the tubular member 12 may comprise a pair of annular dies 22 and 23 disposed around the end of the tubular member 12 on opposite sides of the cover plate 18 and held in a suitable clamping fixture adapted to produce squeezing force on the dies. The die 23 comprises two semicircular segments adapted to be fitted around the tubular member 12 inwardly of the cover plate 18 and held in the clamping fixture in encircling relation to the tubular member. The dies 22 and 23 are formed with annular V- shaped ribs 24 and 25 adapted to engage the surfaces of the cover plate at annular opposing narrow areas spaced a short distance radially outwardly from the opening 26 in the cover plate through which the insulating sleeve 36 and the tubular member 12 are inserted. When inward squeezing force is applied to the dies 22 and 23, the metal of the cover plate bulges inwardly at the interior portion of the opening 26, as shown at 27 in Figure 4, transmitting squeezing force to the relatively deformable insulating sleeve 36. The ends of the sleeve 36 are confined in the annularly recessed inner portions 37 and 38 of the dies, whereby endwise expansion of the sleeve is prevented, and whereby the squeezing force is transmitted through the material of the sleeve to the wall of the tubular member 12. As shown in Figure 4, the inward bulge 27 of the wall of opening 26 produces a similar inward bulge of Patented Mar. 12, 1957 Heatthe insulating sleeve 36, and the squeezing force transmitted through the bulge of the sleeve 36 causes the metal of the tubular member 12 to flow laterally away from the` bulge,v inward deformation of the tubular member being prevented by the'densely compacted internal insulating material 15; The' resultant joint has substantially the cross-sectional shape shown in Figures 1 and 4,v and itV will be apparent from these gures that the metal of the cover plate has been placed in intimate sealing'contact alongV a substantialarea with` the inward-ly deformed portion of sleeve 36,V and that said inwardly deformed sleeve portion has been similarly placedin intimate sealingl contactwith the inwardly deformed outer wally surface of the tubular member along a substantial area, thereby providing the desired liquid-tight, electrically insulated joint, as well as providingA a connection having great mechanical rigidity.

In assembling a heating unit such as is illustrated in Figure l., theY following procedure is employed:

l. Thel heating. windings with their rod-like terminals attached are placed in straight tubes and the tubes are lledfwith the powdered insulating material, such as magnesium oxide; The magnesium oxidel is packed to a moderate density by vibrating the tubes during lling.

2. The tubes are squeezed by being passed through reducing dies, to thereby pack the insulating material to a rock-like density.

3'.` The tubes are bent to U-shape.

4; The cover plates 18 and insulating sleeves 36 are then pressure-sealed to the end portions of the tubes by i the process above described.

5. The procelain spacers 17 are then placed around the rod-like terminals 14 of the heatingl windings.

6. The terminal lugs 35 are then placed on the rod-like elements 14 and are then pressure-locked thereto by deforming the lugs inwardly to produce the flat surfaces 16.

As shown in Figure 5, the cover plate 18 may be pressure-sealed to the end portions of the tube 12 by the process above described at a substantial distance from the ends of the tube, and, as a final step, an insulating block 37 of heat-resisting, electrically insulating material may be pressure-fitted on said end portions, to derive the iinal structure shown in Figure 5, wherein the insulating block 37 serves as an insulating spacer as well as a mechanical strengthening member to rigidity the structure ofthe unit adjacent the cover plate 18.

While certain specic embodiments ofan improvedmethod of assembling. an insulated immersion-type electricalf heating unit have been disclosed in the foregoing description, it will be understood that various modifications y within: the spirit of the invention may occur to those skilled in the art. Therefore it is intended that no limitations be placedl on the inventionexceptfas deiin'ed by the scope of the appended claims.

What is claimed is:

l. A method of forming a liquid-tight, electrically insulated, mechanical connection between a metalcover plate and an electrical heating element of the type comprising a metal tubular member surrounding aresistance unit, with densely packed granular insulation material between the resistance unit and the internal surface of the tubularmember, comprising inserting a sleeve element of relatively deformable insulating material throughy an opening inthel cover plate, inserting the heating element through the sleeve element, and exerting'localized squeezing pressure on the annular areaY of the plate around and adjacent said opening, said squeezing pressure being applied uniformly and only to a narrow continuous annular area concentric with and spaced outwardly a suflicient distance from sai-d opening so that the annular mass of metaly of the plate outwardly adjacent the tubular lmember which is' subjected to the squeezing pressure is forced inwardly against the intermediate portion of the sleeve elementV til) annular mass to ow inwardly and to cause suicient inward deformation of the sleeve element to locally reduce the wall thickness of the tubular member continuously around said tubular member, inward deformation of the tubular member being prevented by the densely packed granular insulating material therein.

2. A method of forming a liquid-tight, electrically insulated mechanical connection between a metal cover plate and an electrical heating element `of the type comprising a metal tubular member surrounding a resistance unit, with densely packed granular insulation material` between the resistance unit and the internal surface of the tubular member, said insulation material having a rocklike consistency, comprising inserting a sleeve element of relatively deformable insulating material through an opening in the cover plate, inserting the heating element through the sleeve element, and exerting localized squeezing pressure on the annular area of the plate around and adjacent the ends of the' sleeve element while coniining said ends against endwise expansion, said squeezing pressure being applied uniformly and only to a narrow continuous annular area concentric with and `spaced outwardly a suiiicient distance from the ends of the sleeve element so that the annular mass of metal of the plate outwardly adjacent the tubular member which is subjected to the squeezing pressure is forced inwardly against the intermediate portion of the sleeve element and is transmitted by the sleeve element to the tubular member, the squeezing force being sufficient to cause saidY annular mass to flow inwardly and to cause suflicient inward deformation of the sleeve element to locally reduce the wall' thickness of the tubular member continuously around said tubular member, inward radial deformation of the tubular member being prevented by the densely packed granular insulating. material therein.

3. A method of forming an insulated electrical heating element of the liquid immersion type includingl a metal cover plate and a metal tubular member surrounding a helical resistance element, with granular electrically insulating, heatconducting material between the resistance element and the tubular member, comprising placing the' resistance element axially in the tubular member, fillingl the tubular member with the granular material, passing the tubular member through reducing dies to reduce its diameter andV pack the granular material to a rock-like density suicient to `oppose inward deformation of the tubular member, bending the tubular member so that its ends are substantially parallel, inserting sleeve elements of relatively deformable insulating material through openings inthe cover plate', inserting said ends throughv said sleeve elements, and exerting localized squeezing pressure on annular areas of the plate around and adjacent the ends of the sleeve members while conining said lastnam'ed ends against endwise expansion, `said squeezing pressure being uniformly applied and to only opposed continuous narrow annular areas concentric with Iandy spaced outwardly a Asutlicient distance from said lastnamed ends :so'that the respective annular masses of the metal of the plate outwardly adjacent the tubular memlber which arev subjected tothe squeezingV pressure are forced inwardly against thei intermediate portions of the 'sleeve elements, the squeezing force being suicient to cause said annular masses to iiow inwardly andf to cause suiicient inward deformationl of the sleeve elements to locally reduce the wall thickness of the tubular member continuously around said tubular member, inward radial deformation of the tubular member being prevented by the densely packed granular insulating material therein, andi whereby a` continuous, insulated, liquid-tight sealv is formed between the cover plate and the ends of the tubular member.

4. lnan electrical heating unit, a metal cover plate, ay metal tubular member containingl a resistance unit and tightly packed, rock-like insulation material, said tubular member extending through said cover plate, and a sleeve element of `relatively deformable insulating material sealingly `secured between the tubular member and the cover plate and being inwardly deformed at its intermediate portion.

5. In an electrical heating unit, a metal cover plate, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said `tubular member extending through said cover plate, and a sleeve element of relatively ldeformable insulating mate-rial sealingly secured between the tubular member and the cover plate and being inwardly deformed at its intermediate portion as a result of squeezing pressure applied `on the opposite sides of :the cover plate.

6. In an electrical heating unit, a metal cover plate, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said tubular member extending through said `cover plate, and a sleeve element of relatively deformable insulating material sealingly Vsecured between the tubular member and the cover plate and being inwardly deformed at its intermediate portion as a result of squeezing pressure applied on a portion of the cover plate.

7. In an electrical heating unit, a metal cover plate, a metal tubular member containing la resistance unit and tightly packed, rock-like insulation material, said tubular member extending through said cover plate, and a sleeve element of relatively deformable insulating material sealingly secured between the tubular member and the cover plate and being inwardly deformed at itsinterrnediate portion as a result of squeezing pressure applied on opposite portions of the cover plate ladjacent the tubular member.

8. In an electrical heating unit, a metal cover plate, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said tubular member extending ythrough said cover plate, and a sleeve element of relatively deformable insulating material sealingly secured between the tubular member and the cover pla-te and being inwardly deformed at its intermediate portion by an inwardly deformed portion of the cover plate adjacent the tubular member.

9. yIn an electrical heating unit, a metal cover plate, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said tubular member extending through said cover plate, and a sleeve element of relatively deformable insulating material sealingly secured between the tubular member vand the cover plate and being inwardly deformed at its intermediate portion by opposed inwardly deformed portions of the cover plate.

l). In an electrical heating unit, a metal cover plate, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said tubular member extending through said cover plate, and a sleeve element of relatively deformable insulating material sealingly secured between the tubu-lar member and the cover plate .and being inwardly deformed at its intermediate portion by opposed inwardly deformed annular portions of the cover plate.

ll. In an electrical heating unit, a metal cover plate, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said tubular member extending through said cover plate, and a body of relatively deformable insulating material sealingly secured between the tubular member and cover plate and being inwardly deformed at its intermediate portion by an inwardly deformed portion of the cover plate adjacent the tubular member.

l2. =In an electrical heating unit, a metal cover plate member, a metal tubular member containing a resistance unit and tightly packed, rock-like insulation material, said tubular member extending through the cover plate member, and a relatively deformable insulating member sealingly secured 'between said cover plate member and tubular :member and being inwardly deformed at its intermediate portion by an inwardly deformed portion of at least one of said members.

References Cited in the tile of this patent UNITED STATES PATENTS 1,734,925 Tovey Nov. 5, 1929 1,916,804 McNab July 4, 1933 2,473,669 White June 21, 1949 2,670,529 Thomas Mar. 2, 1954 

